Marek's disease virus (MDV) is an oncogenic avian herpesvirus which induces lymphoma in chicken, its natural host. It is known that non- oncogenic herpesvirus of turkey (HVT) or attenuated strains of MDV can protect chicken against this disease. This is the first known case of successful protection against a naturally occurring tumor of any species. This unique system, i.e. tumor induction and protection in its own host cells, offers an ideal model for the understanding of oncogenesis by herpesviruses. It is our aim to identify the encoded function of the DNA sequences responsible for cellular transformation and tumor induction. Previously we have observed that the majority of viral genomes exist as episomes and the expression of viral genes in those lymphoblastoid cells is quite restricted. Further, we have constructed restriction endonuclease maps of the MDV genome and have identified a potential tumor inducing gene(s) which expressed more abundantly in productively infected cells. Our attention is currently directed toward the latent genes that we consider important for induction and/or maintenance of tumorigenic states of cells. Initially, we will identify the MDV-specific transcripts in MDV induced tumors and in chicken lymphoblastoid cells latently infected with MDV; we will then compare to those in chick embryo fibroblasts (CEF) infected with MDV. Once the transcripts are identified, the precise mapping and sequence of the identified gene will be determined by S1 analysis and cDNA cloning. Finally, we will identify the proteins specified by those latent genes by means of generating specific antibodies to these gene products and immunoprecipitation and/or Western blot analysis by these antibodies.